Steam boiler installations



July 11, 1961 w, DAVIS ETAL 2,991,621

STEAM BOILER INSTALLATIONS Filed Oct. 7, 1957 4 Sheets-Sheet 1 II II I! llll Inventors Q ALLAN VVILUAM DAVIS o ILLIAM 5A MPSON Attorneys July 11, 1961 A. w. DAVIS ETAL STEAM BOILER INSTALLATIONS 4 Sheets-Sheet 2 Filed Oct. 7, 1957 w 7 7 wfi fi fi i 5 :2 AI i 1% MK Wm Invem'grs ALLAN WILL/AM DAV/S w WILLIAM Sagwaom y I Attorney July 11, 1961 w, DAVIS ETAL 2,991,621

STEAM BOILER INSTALLATIONS Filed Oct. 7, 1957 4 Sheets-Sheet 4 Inventors ALLAN WILLIAM DAWJ 3/ WILLIAM SAMPSON ttorneys United States Patent 2,991,621 STEAM BOILER INSTALLATIONS Allan W. Davis, Bearsden, Glasgow, Scotland, and William Sampson, London, England; said Davis assignor to The Fair-field Shipbuilding and Engineering Company Limited, Glasgow, and said Sampson assignor to Foster Wheeler Limited, London, both in Great Britain Filed Oct. 7, 1957, Ser. No. 688,582 I 8 Claims. (Cl. 60-73) This invention relates to steam boiler installations of the type in which superheated steam from a boiler plant is supplied to a steam prime mover assembly having at least two pressure stages and provision for inter-stage re-heating of the steam in its flow from stage to stage.

The invention is a steam boiler installation of the type stated including a steam boiler and a reheater which has a combustion chamber with burner apparatus receiving combustion air in considerable excess and which encloses steam conduits interposed between stages of the prime mover so that the inter-stage steam flowing through these conduits is heated by the gaseous products of combustion, a passage for the main supply of combustion air to the burner apparatus of the steam boiler, an exhaust passage from the reheater combustion chamber to the burner apparatus of the steam boiler for the supplementary supply to this apparatus of the hot gaseous exhaust products in order to utilise their heat and residual oxygen, and automatic control means subject to the influence of the inter-stage steam pressure for shutting off the supply of fuel to the reheater burner apparatus in the event that the flow of inter-stage steam reduces below a predetermined value.

Examples of steam boiler installations of the type stated are illustrated by the accompanying diagrammatic dr in s. which FIG. 1 is a general view of a marine steam boiler and turbine installation forming one example.

FIG. 2 is a sectional view of an automatic fuel supply valve constituting the control means.

FIGS. 3 to 6, illustrate further examples.

In the drawings, the directions in which the oil fuel, the combustion air, the steam and the gaseous exhaust products flow through the various conduits are indicated by arrows, which are drawn in full lines to indicate general and ahead conditions and in dot-ted lines to represent conditions under various contingencies. I

Referring to FIG. 1, the marine steam boiler and turbine installation shown includes a main boiler plant comprising a water-tube boiler with a superheater 11, 11A. The boiler has a furnace-front casing 12 to which air for the oil-fuel burners 13 is supplied through a trunk 14 in order to support combustion in the burners and combustion chamber 15 of the boiler. The installation is connected with a three-stage ahead and twostage astern steam turbine assembly to 24 for the propulsion of the ship. The high and intermediate pressure ahead stages 20, 21 and the high pressure astern stage 23 are arranged in tandem as a turbine unit; the low pressure aheadstage 22 and astern stage 24 are also arranged in tandem, being provided as a separate turbine nnit. The installation'includes an inter-stage reheater 30 which is a tubular heat exchanger. 'I his heat exchanger has a bank of tubes 31 and a combustion ehamber 32 which is shown fitted with an oil-fuel burner 33there may be more than one such burnerand to the furnace-front casing 34 of which combustion air. is supplied in considerable excess. The reheater combustion chamber has an exhaust outlet 35 which is connected by a duct 36 to the trunk 14 leading to the main boiler front casing; the exhausted products are utilised as a preheated gaseous. medium forming a separate supply 2,991,621 Patented July 11, 1961 2 additional to the normal supply of combustion air to the main boiler burners. This arrangement is practicable because the combustion air to the reheater is supplied in considerable excess, so much so that the reheater exhaust gases consist of air and a comparatively small proportion of carbon dioxide. In the example, there is supplied about three times the quantity of air strictly required for complete combustion.

The steam connections are as follows: piping 40 under the control of a stop valve 41, from the superheater 11, 11A of the main boiler 10 to an assembly of turbine control valves consisting of an ahead manoeuvring valve 42, an astern shut-01f valve 43 and an astern manoeuvring valve 44; piping 45 and 46 from the manoeuvring valves 4; and 44 to the high-pressure stages of the ahead and astern turbines; piping 47 from the exhaust of the high-pressure stage of the ahead turbine to the inlet header 48 of the bank of tubes 31 in the reheater 3Q; piping 49 from the outlet header 50 of this bank to the intermediate-pressure ahead stage; piping 51 from this stage to the low-pressure ahead stage; piping 52 from the high pressure astern stage to the lowpressure astern stage. The arrangement of the piping is shown purely diagrammatically; in actual practice, the arrangement would preferably be such that the steam piping 47, 49 between the reheater and the turbine stages is short in length. 7 i The oil fuel supply is by way of piping 58 to the burners 13 of the main boilers and by way of branch piping 59 to the burner or burners 33 of the reheater. The control means for the oil-fuel supply to the reheater is a fuel control valve 60 in the piping 59. This valve has a connection with a control device 61 connected by a braneh pipe 47A with the piping 47 from the highpressnre stage to the reheater. If the steam supply falls below a predetermined limit, the valve 60 is caused by the automatic action of the control device to close and shut off the supply of fuel.

The fuel control valve 60 and the control device 61 used in the present example are shown in FIG. 2. As shown, the valve 60 cgm'prises a chest 62 with a valve seat 63, the valve proper 64, a stem 65 which carries the valve proper and which has a handwheel 66 and a screw-threaded portion 67 for hand operation and which is urged by a spring 68 to close against the seat, and a nut69 which is held against turning by a guide 70 on the chest but is movable up and down with the stem. The chest has oil fuel inlet and outlet branches 71 and 72. The oil supply system is under heavy pressure, for instance about 300 lbs. per square inch, and the pressure of this system forcibly urges the valve proper to close.

The pressure-operated device 61 comprises a cylinder 73 connected by piping 47A to the inter-stage piping 47, a piston 74 which is acted upon by a heavy spring 75 in opposition to the steam pressure, a piston rod 76, and a lever 77 which is pivoted on the nut 69, being notched at 78 to eo-operate with a stop 79 on the valve chest 62, and which is connected to the piston rod. The lever passes into the chest through a slot 80- at the foot of which there is provided a fulcrum 81 for the lever.

Assume that the oil-fuel supply to the reheater is normal, the position of the various parts being as shown in FIG. 2; the valve is held open by the stop 79 acting through the lever 77 and nut 69 on the valve stem 65.

Assume that owing to some contingency there is a serious reduction, or a stoppage, in the flow of steam to the reheater tubes 31. In this event, the piston 74 drops, pulling the lever 77 away from the stop 79 and against the fulcrum 81. Thus, the spring 75 acts through the lever 77 to close the valve, being assisted by the pressure of the Oilon the valve proper 64 and also by the spring 3 68. The valve-closing action is practically instantaneo as soon as the lever 77 is withdrawn, like a trigger, from the stop 79.

Accordingly, the reheater is safeguarded against the contingency that the burners might be maintained in action under conditions, normal or abnormal, when the flow of steam through the reheater tubes is inadequate or has ceased, a contingency which would cause damage or destruction of the reheater tubes. Such conditions occur normally during manoeuvring and during astern propulsron.

The valve 60 cannot be re-opened until after re-establishment of normal steam flow to the reheater and can then be re-opened only by hand operation. Thus, assume re-establishment of normal steam flow; in consequence, the piston 74 is pressed upwards, the opposition of the spring 75 being overcome, so that the lever 77 presses against the side of the stop 79. The engineer turns the handwheel 66 in the valve-closing direction, so that the nut 69 is forced downwards, carrying with it the lever. Eventually the lever notch 78 snaps into engagement with the stop. The engineer now turns the handwheel in the opposite direction, so that the valve 60 is opened by him to whatever extent is considered desirable.

The turbine inter-stage steam connections to the reheater, namely the piping 47 and the piping 49, are interconnected by a bye-pass 85 and have valves 86, 87, 88

. '4 trates, the reheater 30 is encased in an air jacket 105, which incorporates the duct 102 and which serves as an air reservoir from which air is forced through an inlet 106 to the reheater burner apparatus. The fan 100 discharges through an air heater 107 which is similar to the heaters 93, 94 and is supplied by bled-steam piping 95. In the example according to FIG. 1 and FIG. 3, the heating means by which the supplies of combustionair to the main boiler and reheater are preheated have been rdesoribed as comprising the heaters 93 and 94 and the heater 107. As shown, in each instance, there is also provided a socalled steam attemperator or desuperheater, indicated by 108. This is a tubular heat exchanger, the primary purpose of which is to regulate the temperature of the superheated steam from the main boiler 10 to the turbines. This attemperator is interposed in the combustion air trunk 14 or 101 leading from the bledsteam air heater 93 or 107 to the main boiler front casing 12. The superheated steam, being the heating medium of the attemperator, is led through piping 109 which connects the attemperator heating tubes between and in series with the two sections 11 and 11A of the superhea'ter. The attemperator casing is divided into an so arranged that the reheater can be isolated from the 1 steam and combustion systems of the installation for examination, maintenance and repair with merely temporarily adverse influence on the thermal eificiency but with no influence whatever on the technical eifectiveness of the installation.

The combustion air for the main boiler burners and I i the combustion air for the reheater burners or burners may be supplied by separate fans.

Thus, as FIG. 1 shows, the air trunk 14 which leads to the furnace-front casing 12 of the main boiler 10 is supplied with air under pressure by an air fan 90, whereas a separate air fan 91 supplies the casing 34 of the reheater 30 with its combustion air under pressure through a duct 92.

It is desirable that provision should be made for prer heating the supplies of combustion air to both the main boiler 10 and the reheater 30. Thus, the faus 90 and 91 discharge through air heaters 93 and 94, respectively. In the example, both of these air heaters are tubular heat exchangers. The heating medium in each instance is steam bled from an appropriate point in the installation; In the example, the steam is bled from the ahead intermediate pressure stage 21 by piping 95.

Alternatively, a single fan may be used for both supplies, in which event damper gear is provided to regulate 1,

the proportions of the two supplies. Thus, as FIG. 3 shows the single fan 100 supplies a main air trunk 101 leading to the furnace-front casing 12 of the main boiler 10, and a duct 102 branching from the trunk 101 supplies the reheater casing 34. The reheater exhaust outlet 35 opens into a duct 103 leading to the trunk 101, so that this trunk leads the mixture of air direct from the fan 100 and hot air-containing gases from the reheater 30 into the casing 12. A damper 104 in the trunk 101 just beyond where the duct 102 branches from the trunk serves as a means for regulating the proportion of air deflected through the reheater.

, As already specified, the reheater burner apparatus has provision for the admission of combustion air in considerable excess, so that there will be a copious flow through the reheater of gaseous products which are not excessively hot. Thus, there is avoided need for protection of the reheater tubes by water-tubed walls or other cooling means. It is preferable, however, to encase the reheater in a cooling jacket for preheating its own combustion air or other supply of combustion air to the main or other boiler of the installation. Thus, as FIG. 3 illusattemperating chamber and a bye-pass 111, respectively provided with inter-locked dampers 110A and 111A. By operation of these dampers the flow of air through the attemperating chamber 110 can be regulated. Under manoeuvring conditions, when the consumption of steam by the turbines is reduced, it may be advantageous to direct the superheated steam through the attemperating chamber in order to cool the steam, the heat of which might otherwise become excessive. Apart from manoeuvring conditions, the attemperator is available as an economic means of preventing excessive rise in the temperature of the superheated steam from the main boiler.

. In each of the examples illustrated by FIGS. 1 and 3, the exhaust outlet of the reheater is connected to the normal trunk for the supply of combustion air to the main boiler-front casing, so that the reheater exhaust gases will intermingle with the normal combustion air and both supplies will enter the front casing and pass to the burners as a hot gaseous mixture. If desired, there may be incorporated in the combustion air system appropriate means for mixing both supplies. Thus, as FIG. 4 illustrates, there is incorporated inthe installation a fan 112, a bled-steam air heater 1 13, an attemperator 114, a main air trunk 115 leading to the main boiler 10, a branch duct 116 leading to the reheater 30, an airapportioning damper 1 17 and an exhaust duct 118 from .the reheater. The installation is provided with a mixing means comprising a cylindrical mixing chamber 119 having a series of internal co-axial convergent baffles 119A. The main trunk 115 leads co-axially into the chamber, whereas the duct 118 from the reheater leads laterally into the chamber, and the hot gaseous mixture passes .axially from the chamber by way of the main trunk 1-15 to the front casing 12. Such mixing means ensures that the gas-air mixture is supplied to the main boiler burners in a uniformly mixed condition.

In the example described with reference to FIG. 1, an auxiliary fan- 91 is provided as a means of supplying to the reheater combustion air independent of the normal combustion air supply to the main boiler. Instead, an auxiliary fan may be provided as a booster; that is to say, the total combustion air system is supplied by a singlefan and a booster fan is incorporated in a branch supply to the reheater.

An example of such an arrangement is shown in FIG. 5. As shown, the single main fan 90 delivers combustion air through air heaters 93, 108 to the main air trunk 122 leading to the main boiler-front casing 12. A branch duct 123 from the main trunk leads pre-healted air to the inlet of a booster 124, namely a fan which boosts the "supply of air flowing through the branch duct 123 from the mainv the discharge r nch 5. .th oos leading into the front casing. 24 of the rehea er 0- T e hot exhaustgaseous products from the reheater are led by a duct, 126 into the main trunk and are supplied to the casing 12 in admixture with the preheated normal combustion air. The proportion of the'air deflected to thereheater can, be controlled by regulating the speed of the booster fan in relation to the fan speed. The booster fan serves to. increase to a selected magnitude the pressure of the air supplied to the reheater.

FIG. 6 illustrates a modification of the example illustrated by FIG. 5,. According to this modification, the pre-heated combustion air supply to the reheater is divided into a primary supply forced under booster pressure and a secondary supply under a lower pressure. As shown, thereheater supply duct 125 is partitioned by a ba'fiie 130 and is continued as branches 131 and 1312. The branch 131 leads into the inlet of the booster fan 114, the discharge branch of which is connected to a central air inlet 133, which therefore is supplied with air under the increased booster pressure and delivers this air as a centralstream ofprimary air to the reheater burner apparatus 33. The other branch 13-2 leads into an outer air inlet 134, which surrounds the central inlet 136. This outer inlet. supplies the secondary air under much lower pressure. The arrangement is such that the primary air satisfies the requirements of the burner 33 as regards combustion, whereas the secondary air is utilised mainly as a coolingmedium to prevent excessive heatingot the reheater tubes.

The examples described may be carried out in practice in any of various ways, for instance:

The installation may consist of two or more main boilers to the burners of any one or more of which the reheater exhaust outlet may be ducted, and provision may be made for directing the exhaust gases to any one or more of these burners at choice;

The installation may include an auxiliary boiler to the burners of which the reheater exhaust outlet is also connected;

The reheater may be supplied with exhaust gases from one or more diesel or other internal combustion engines as its combustion-supporting medium;

A reheater such as hereinbefore described may be used to reheat more than one inter-stage steam flow in the same turbine, which ordinarily will have a stage from high pressure to intermediate pressure and a stage from intermediate pressure to low pressure;

Where the boiler installation is associated with two or more turbine assemblies, each such assembly may have its own inter-stage reheater or one reheater may be used incorporating two or more separate banks of tubes, there being one bank for each inter-stage steam flow;

The fuel to the reheater burners may be liquid or gaseous or a pulverised solid, so long as its flow is capable of immediate stoppage by automatic control means;

Means may be provided for controlling automatically or manually the ratio between the reheater exhaust gas supply and the normal combustion air supply;

In order to avoid the contingency that the reheating becomes excessive, means may be provided for regulating the supply of the oil fuel and combustion air to the reheater in accordance with the temperature of the interstage steam leaving or entering the reheater, and such means may be automatic and/or manual.

Although in the examples described with reference to the drawings it is a marine steam boiler installation connected with a propulsion turbine assembly that is described, the invention is equally applicable to land boiler installations.

We claim:

II. A steam power plant comprising -a steam boiler which includes burners, a reheater which includes a combustion chamber with burner apparatus, tubing exposed 6 to the products of, combustion of said apparatus and control means for the supply of fuel to said burner apl' ar-a tus, means including a trunk for'the main supply of com bustion air to the steam boiler burners, means for; supplying combustion air in considerable excess'to the "ref heater burner apparatus, a duct leading fromthe reheater combustion chamber to said trunkjto supplement said main supply of combustion air with the hot gaseous exhaust products to. utilize their heat and residual o'xy gen, said duct communicating with said trunk upstream from said burners to provide a uniform mixture of the exhaust products, residual oxygen and combustion air a steam prime mover assembly receiw'n-g its steam supply from the steam boiler and having at least two pressure stages, a conduit for the passage of inter-stage steam connected beween said stages, said reheater tubing being interposed in said conduit, and an automatic control device connected to said conduit and haying a trigger means responsive only to a predetermined an in pressure of the inter-stage steam in said conduit and operatively connected with said fuel control means to shut off the reheater fuel supply following such a fall said fuel control means including a hand operated mechanism capable of restoring the reheater fuel supply only after, t e-establishment of normal pressure or the interstage steam.

2. A, steam power plant comprising a steam boiler which includes burners, a reheater which includes a combustion chamber with burner apparatus and re-heater tubing exposed to the products of combustion of said apparatus, fan means for the main supply of combustion air to the steam boiler burners and to the reheater burner apparatus in considerable excess, a trunk leading from said tan means to the steam boiler burners, a branch leading from said trunk to the reheater burner apparatus, an exhaust duct leading from the reheater combustion chamber back to said trunk to supplement said main supply of combustion air with the hot gaseous exhaust products to utilize their heat and residual oxygen, said exhaust duct communicating with said trunk upstream of said burners to provide a uniform mixture of the exhaust gases, residual oxygen and combustion air a steam prime mover assembly receiving its steam supply from the steam boiler and having at least two pressure stages and a conduit for the passage of inter-stage steam connected between said stages, said reheater tubing being interposed in said conduit.

3. A steam power plant according to claim 2 including also a secondary branch from the main trunk to the reheater burner apparatus for the supply thereto of secondary air.

4. A steam power plant according to claim 2, including also an air heater through which the main combustion air supply to the steam boiler burners is passed and pre-heated, and steam piping from the steam prime mover assembly to said air heater for the supply thereto of air heating steam.

5. A steam power plant according to claim 2, in which the steam boiler has a superheater connected to the prime mover assembly for the supply thereto of superheated steam, and including an attemperator through which the main combustion air supply to the steam boiler burners is passed and pro-heated, and piping connecting the superheater to said attemperator so as to supply thereto superheated steam as the air-heating medium of the attemperator and so as to utilize the air passing therethrough to prevent excessive temperature conditions in the superheated steam.

6. A steam power plant comprising a steam boiler which includes burners, a reheater which includes a combustion chamber with burner apparatus and tubing exposed to the products of combustion of said apparatus, fan means for the main supply of combustion air to the steam boiler burners and for supplying combustion air in considerable excess to the reheater burner apparatus,

a main air trunk leading from the fan means to the steam boiler burners, mixing means interposed in said main air trunk upstream from said burners to provide a uniform mixture of exhaust gases, residual oxygen and combustion air, an exhaust duct leading from the reheater combustion chamber to said mixing means for admixture therein with the main combustion air supply to supplement this supply with the hot gaseous exhaust products to utilize their heat and residual oxygen, a steam prime mover assembly receiving its steam supply fromthe steam-boiler and having at least two pressure stages and a conduit for the passage of inter-stage steam connected between said stages, said reheater tubing being interposed in said conduit.

7. A steam power plant comprising a steam boiler which includes burners and a superheater, a reheater which includes a combustion chamber with burner apparatus and re-heater tubing exposed to the products of combustion of said apparatus, means including a trunk for the main supply of combustion air to the steam boiler burners, means for supplying combustion air in considerable excess to the reheater burner apparatus, a duct leading from the reheater combustion chamber to said trunk to supplement said main supply of combustion air .with the hot gaseous exhaust products to utilize their heat and residual oxygen, said duct communicating with said trunk upstream of said burners to provide a uniform mixture of the exhaust gases, residual oxygen and combustion air a steam prime mover assembly having at least two pressure stages, piping from said superheater to said prime mover assembly for the. supply thereto of super- .heated steam, an air pre-heater interposed in said main supply trunk and piping from said superheater to said air pre-heater to provide superheated steam as the air,- heating medium said air pre-heater serving'als'o to prevent excessive superheating of the steam supplied through said piping to the prime mover, and a conduit'for 'the passage 'of inter-stage steam connected between said stages, said reheater tubing being inter-posed in said conduit.

8. A steam power plant according to claim 7, including also control means for the supply of fuel to the reheater burner apparatus and an automatic control device connected to said conduit and responsive to a predetermined fall in pressure of the inter-stage steam in said conduit, said device being operatively connected with said fuel control means to shutoff the fuel supply following such a fall and said fuel control means including a hand-operated mechanism capable of restoring the fuel supply only after re-establishment of normal pressure of the inter-stage steam.

References Cited in the file of this patent UNITED STATES PATENTS 

